One type of fuel injector that is used for injecting fuel into an internal combustion engine comprises a valve element in the form of a needle that is reciprocated by an operating mechanism to seat on and unseat from a valve seat member thereby alternately closing and opening a passageway through it. For aiding in guiding the reciprocation of the needle, a needle guide member is disposed proximate the valve seat member.
The present invention relates to a new way to join a needle guide member and a valve seat member together.
First, it should be recognized that certain needle guide members and valve seat members are already commonly joined by using machined fixtures, pressing, clamping, laser welding, or resistance welding. Welding of a needle guide member to a valve seat member in a precise locating fixture is superior to other methods in cost and/or precision. Resistance welding works well when the design of the components is suitable and the contact area is small. The present invention solves the problem of welding these components when their design is not suitable for the previous techniques.
Because of valve functional requirements, the design of the two components for which the present invention has been developed requires that they have relatively large flat surface areas that mutually abut. They cannot be successfully resistance welded because the manufacturing techniques employed to fabricate them do not consistently produce surfaces of sufficient flatness for resistance welding to be suitable. Attempts to resistance weld these surfaces are apt to result in distortions of the components which although seemingly small are nevertheless sufficiently large that they may impair proper functionality of a precision device like a fuel injector.
The present invention comprises creating raised projections in one of the two parts for abutting the other part preparatory to applying current through the abutted parts. The projections concentrate the welding energy for producing resulting strong welds while reducing the total weld energy used so that the parts do not distort to a degree that impairs their proper functionality in a fuel injector. They provide consistent, well-defined contact areas so that the welds can be consistently accurate placed at desired circumferential increments around the co-axis of the two abutted parts. Three projections are used so that three-point abutment is consistently assured irrespective of slight irregularities in flatness of the surface containing them and in flatness of the surface which they abut.
The creation of the projections by machining is not economical. Molding and coining are the preferred ways to create them. It is also possible for projections to be provided in a separate part that is disposed between the valve seat member and the needle guide member so that projections engage both parts.
Details of a presently preferred embodiment of the invention will be described with reference to the following description which is accompanied by the following drawings presenting the best mode for carrying out the preferred embodiment at this time.